quarta-feira, 13 de abril de 2011

Bacterioides

Bacteroides species are anaerobic bacteria that are predominant components of the bacterial florae of mucous membranes[1] and are therefore a common cause of endogenous infections. Bacteroides infections can develop in all body sites, including the CNS, the head, the neck, the chest, the abdomen, the pelvis, the skin, and the soft tissues. Inadequate therapy against these anaerobic bacteria may lead to clinical failure.

Because of their fastidiousness, they are difficult to isolate and are often overlooked. Their isolation requires appropriate methods of collection, transportation, and cultivation of specimens.[2] Treatment is complicated by 3 factors: slow growth, increasing resistance to antimicrobial agents,[3] and the polymicrobial synergistic nature of the infection.[4]

The B fragilis group, a member of the Bacteroidaceae family, includes B fragilis (causes the most clinical infections), Bacteroides distasonis, Bacteroides ovatus, Bacteroides thetaiotaomicron, and Bacteroides vulgatus. These bacteria are resistant to penicillins, mostly through the production of beta-lactamase. They are part of the normal GI florae[1] and predominate in intra-abdominal infections and infections that originate from those florae (eg, perirectal abscesses, decubitus ulcers). Enterotoxigenic B fragilis (ETBF) is also a potential cause of diarrhea.[5]

Pigmented Prevotella, such as Prevotella melaninogenica and Prevotella intermedia (which were previously called the Bacteroides melaninogenicus group), Porphyromonas (eg, Porphyromonas asaccharolytica), and nonpigmented Prevotella (eg, Prevotella oralis, Prevotella oris) are part of the normal oral and vaginal florae and are the predominant AGNB isolated from respiratory tract infections and their complications, including aspiration pneumonia, lung abscess, chronic otitis media, chronic sinusitis, abscesses around the oral cavity, human bites, paronychia, brain abscesses, and osteomyelitis. Prevotella bivia and Prevotella disiens (previously called Bacteroides) are important in obstetric and gynecologic infections

Bacteroides is a genus of Gram-negative, bacillus bacteria. Bacteroides species are non-endospore-forming, anaerobes, and may be either motile or non-motile, depending on the species.[1] The DNA base composition is 40-48% GC. Unusual in bacterial organisms, Bacteroides membranes contain sphingolipids. They also contain meso-diaminopimelic acid in their peptidoglycan layer.

Bacteroides are normally mutualistic, making up the most substantial portion of the mammalian gastrointestinal flora,[2] where they play a fundamental role in processing of complex molecules to simpler ones in the host intestine.[3][4][5] As many as 1010-1011 cells per gram of human feces have been reported.[6] They can use simple sugars when available, but the main source of energy is polysaccharides from plant sources.

One of the most important clinically is Bacteroides fragilis.

Bacteroides melaninogenicus has recently been reclassified and split into Prevotella melaninogenica and Prevotella intermedia.[7]

PathogenesisBacteroides species also benefit their host by excluding potential pathogens from colonizing the gut. Some species (B. fragilis, for example) are opportunistic human pathogens, causing infections of the peritoneal cavity, gastrointestinal surgery, and appendicitis via abscess formation, inhibiting phagocytosis, and inactivating beta-lactam antibiotics.[8] Although Bacteroides species are anaerobic, they are aerotolerant and thus can survive in the abdominal cavity.

In general, Bacteroides are resistant to a wide variety of antibiotics — β-lactams, aminoglycosides, and recently many species have acquired resistance to erythromycin and tetracycline. This high level of antibiotic resistance has prompted concerns that Bacteroides species may become a reservoir for resistance in other, more highly-pathogenic bacterial strains.[9] [10]